The present invention relates to fluid flow control apparatus and more particularly, but not exclusively, to such apparatus that is used to control the flow of pneumatic or hydraulic fluid to a valve actuator.
In many applications it is desirable to automate the actuation of a pipeline valve such as, for example, an emergency shut-down valve, via a remote control system. This is particularly necessary in harsh environments such as, for example, a petrochemical pipeline located on land or off-shore. Such a valve may be of any suitable form such as, for example, a rotary ball valve, a butterfly valve or a gate valve. The actuation of the valve in such a pipeline is often effected by an actuator for controlling the position of the valve by acting on the valve stem. The control fluid is typically pneumatic or hydraulic as there is usually a readily available source at the location. It is supplied to the actuator (or an intervening valve positioner that operates the actuator) via a control valve whose operation is controlled by a fluid pressure pilot signal that is selectively delivered when the status of associated logic control valves allow. Each of the logic valves is connected into the control fluid flow line and is individually controllable manually and/or automatically. The internal configuration of the logic control valves can take any suitable form as can their manner of operation. Examples include solenoid-operated valves, valves that are manually operable by a push-pull plunger, key-operated valves or pilot fluid valves, each of which may be normally open or closed and each of which may be lockable in one or more positions.
The configuration and arrangement of the main control valve and the logic control valves (often referred to as “directional” control valves) in the system is dependent on the particular application and the customer's requirements in terms of safety and the logic conditions that have to be satisfied for operation of the actuator. The valves can be linked together to create many different complex circuits and in view of the large number of valve permutations, the design and manufacture of the control apparatus is generally tailored to meet the specification and requirements of the particular application and is therefore relatively expensive. The installation, servicing, and maintenance of such apparatus also tend to be relatively complex.
It is an object of the present invention to obviate or mitigate the above, and other, disadvantages.